Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $230.83   9.138%   $251.9232   $251.92   $251.90   $251.90  
  Purchase #2 $38.90   13.146%   $44.0138   $44.01   $44.00   $44.00  
  Purchase #3 $215.84   9.202%   $235.7016   $235.70   $235.70   $235.70  
  Purchase #4 $90.32   5.612%   $95.3888   $95.39   $95.40   $95.40  
  Purchase #5 $71.27   10.131%   $78.4904   $78.49   $78.50   $78.50  
  Purchase #6 $195.46   5.545%   $206.2983   $206.30   $206.30   $206.30  
  Purchase #7 $168.49   8.748%   $183.2295   $183.23   $183.25   $183.20  
  7 purchase totals = $1,011.11       $1,095.0456   $1,095.04   $1,095.05   $1,095.00